Effect of heat treatment on the Laser Powder Bed Fused (L PBFed) 18Ni300 maraging steel

Abstract

Long-term performance of galvanic anodes for protection of steel reinforced concrete structures

Long-term performance of galvanic anodes for the protection of steel reinforced concrete structures

The present work focuses on the characterization of maraging steel 300, fabricated through the Laser-Powder Bed Fusion (L-PBF) process. The study investigates the microstructural features, microhardness, and scratch resistance of both the as printed and the heat treated samples. At the as printed state, microstructural analysis reveals the presence of distinct scan tracks, melt-pool boundaries and fine dendritic/ cellular structures, formed due to the rapid cooling associated with the L-PBF process. The study onto the XY and XZ planes of the rectangular cuboid part demonstrates non-uniform microstructural morphology as influenced by the local thermal gradients and cooling rates, during the layer-wise fabrication schedule. The post-heat treated specimens exhibit relatively more homogeneous microstructures due to the solution treatment, which is attempted prior to the aging treatment. Microhardness testing shows a substantial increase in the microhardness value after the heat treatment. The increase in the microhardness value is greatly attributed to the precipitation hardening that occurs during the aging treatment. Scratch testing further demonstrates that the heat treated specimen possesses improved scratch resistance, a lower penetration depth and thereby better resistance to surface deformation under constant loading condition. The enhanced tribological performance is directly related to the increased microhardness value (due to the effect precipitation strengthening) obtained after the ageing treatment. The outcomes of this investigation clearly show the correlation between the microstructural evolution and mechanical properties of maraging steel fabricated through the L-PBF process. The findings infer that the microhardness and scratch resistance of the L-PBFed maraging steel are enhanced by the post-processing heat treatment, making it an appropriate candidate for advanced engineering applications requiring high strength and surface durability.